9 lines
299 B
Text
9 lines
299 B
Text
import logic
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open tactic
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theorem tst (a b : Prop) (H : a ↔ b) : b ↔ a
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:= have H1 [fact] : a → b, -- We need to mark H1 as fact, otherwise it is not visible by tactics
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from iff.elim_left H,
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by apply iff.intro;
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apply (assume Hb, iff.elim_right H Hb);
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apply (assume Ha, H1 Ha)
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